Method for manufacturing bimetal

ABSTRACT

A bimetal is disclosed having a high, rapid deflection over a specified temperature range, including a high expansion metal alloy component having a high thermal expansion coefficient that changes rapidy at 50×10 -6  /°C. or greater at a temperature of between about 100° C. and 250° C. and containing from 15-30% by weight of manganeses, the balance of iron. The second component has a substantially constant thermal expansion coefficient regardless of the temperature change, and is preferably a stainless steel. These bimetals are used in circuit breakers, thermal protectors and the like.

This is a division of application Ser. No. 880,301 filed Feb. 22, 1978now U.S. Pat. No. 4,207,381.

BACKGROUND OF THE INVENTION

This invention relates to a bimetal and more particularly to a bimetalwhich is rapidly deflected at an optionally specified high temperatureand indicates a satisfactory reversible behavior depending ontemperature change.

The deflection of the prior art bimetal generally proceeds at asubstantially fixed rate in proportion to temperature change. Where,therefore, it was desired to use the known bimetal in such applicationas required the bimetal to make a rapid deflection over a prescribedtemperature range, for example, the application where a bimetal wasdirectly used in a contact drive mechanism, it was necessary to providean additional quick responsive drive mechanism. The quick responsivedrive mechanism includes, for example, a repulsion board, magnet orspring. A combination of a bimetal and any of these quick responsivedrive mechanisms enabled the original slow deflection of the bimetalitself to be carried out quickly. However, a bimetal device which wasprovided with the above-mentioned quick responsive drive mechanism hadthe drawbacks that the bimetal device as a whole becomes bulky and hadto be manufactured with a complicate design.

The known bimetal indicating a rapid deflection over a certaintemperature range includes martensite transformation such as an Ni-Tialloy utilizing a shape memory effect. This shape memory type alloy hasto be deformed under a specified temperature condition before being usedas a bimetal. And, said shape memory type alloy does not indicate thesame rate of deflection when used frequently, failing to be effectivelyused in practice. Moreover, the above-mentioned type of bimetal had thedrawbacks that it indicated a rapid deflection at a relatively lowtemperature, and had insufficient workability and bandability,presenting difficulties in manufacture.

A bimetal rapidly deflectable at a specified temperature is generallyused for temperature control of household electric appliances and as asafety device for various industrial apparatuses. Therefore, theabove-mentioned bimetal is desired to have as high an anticorrosiveproperty as possible.

SUMMARY OF THE INVENTION

It is accordingly an object of this invention to provide a novel bimetalwhich makes a rapid deflection over a specified temperature rangewithout the aid of the aforesaid quick responsive drive mechanism, thatis, a bimetal whose high expansion layer is prepared from the knowniron-manganese alloy containing manganese causing the resultant bimetalto have a high thermal expansion coefficient, and indicates prominentworkability and bondability and a satisfactory reversible behaviorrelative to temperature change.

Another object of the invention is to provide a novel bimetal of theabove-mentioned type which is further rendered anticorrosive.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a vertical sectional view of bimetal according to thisinvention; and

FIG. 2 shows the deflection of the free end of the bimetal of thisinvention relative to temperature change and that of the prior artbimetal.

DETAILED DESCRIPTION OF THE INVENTION

A bimetal according to this invention comprises a first alloy componentwhich rapidly indicates a deflection greater than 50×10⁻⁶ /°C. at anoptionally specified high temperature, and a second alloy componentwhich is bonded to the first alloy component and whose thermal expansioncoefficient remains substantially fixed relative to temperature change.The second alloy component has substantially the same thermal expansioncoefficient as that which is indicated by the first alloy component at atemperature lower than that at which the thermal expansion coefficientof said first alloy component rapidly increases.

The first alloy component is formed of 15 to 30% by weight of manganeseand substantially iron as the remainder. Or the first alloy component isprepared from 15 to 30% by weight of manganese, and a member selectedfrom the group consisting of 2 to 15% by weight of chromium, 2 to 15% byweight of cobalt and 2 to 20% by weight of a mixture of chromium andcobalt, and substantially iron as the remainder.

The first alloy used as the high expansion component of the presentbimetal has its composition specifically restrictively defined for thefollowing reasons.

Manganese is an important element to increase the thermal expansioncoefficient of a bimetal and also cause the thermal expansioncoefficient to be rapidly varied relative to temperature change. Theamount of manganese needed to cause the thermal expansion coefficient tobe rapidly varied at an optionally specified temperature ranges from 15to 30% by weight, and preferably 15 to 25% by weight. The thermalexpansion coefficient of a bimetal indicates a value of approximately50×10⁻⁶ to 400×10⁻⁶ /°C. near that point included in the above-mentionedrange of the manganese content at which a rapid change occurs in thethermal expansion coefficient.

Chromium is an important element in a bimetal having high anticorrosiveproperty. The amount of chromium required to improve the anticorrosiveproperty is selected to be over 2% by weight. The amount of needed tolet the thermal expansion coefficient of a bimetal fall within theabove-mentioned range has been found to be less than 15% by weight.Therefore, the prescribed content of chromium is set between 2% and 15%by weight.

Cobalt has the same function as chromium, and its content is alsopreferred to range from 2% to 15% by weight for the reason given above.

With this invention, it is possible to use both chromium and cobalt forimproving the anticorrosive property of a bimetal. In this case, it ispreferable advised to mix both elements in a total amount larger than 2%by weight in order to increase the anticorrosive property of a bimetal.Further, the total content of a mixture of chromium and cobalt should beless than 20% by weight or preferably 15% by weight.

Impurities are unavoidably carried into the raw materials of the presentbimetal such as carbon, oxygen, nitrogen, sulphur, phosphorus, andaluminium or silicon purposely added as a deoxidant at the time ofdisolution of the raw materials will not obstruct one effect of thebimetal according to this invention, provided the total amount of allthese materials is less than 1% by weight. Nickel, known as an elementadapted to increase the anticorrosive property of a bimetal will notreduce the effect of the present bimetal, provided the nickel content issmaller than 3% by weight.

The second alloy constituting the low thermal expansion component of thebimetal of this invention is formed of Invar, for example, aniron-nickel system (the nickel proportion ranging between 36% and 50% byweight). The second alloy is preferred to be the type whose thermalcoefficient remains substantially fixed near that temperature at whichthe thermal expansion coefficient of the first alloy constituting thehigh thermal expansion component of the present bimetal commences toincrease rapidly, and further is smaller than the increased thermalexpansion coefficient of the first alloy.

The second alloy of low thermal expansion should preferably be preparedfrom an alloy having substantially the same thermal expansioncoefficient as that which is indicated by the first alloy of highthermal expansion at a lower temperature than that at which the thermalexpansion coefficient of said first alloy begins to increase rapidly,for example, austenitic stainless steel such as SUS304, SUS310.Application of the second alloy of the above-mentioned type prominentlyincreases the effect of this invention.

This invention will be more fully understood by reference to theexamples which follow.

EXAMPLE 1

First, experiments were made on the deflection of a bimetal relative totemperature change to examine its behavior characteristics. For theseexperiments, alloys having the compositions shown in Table 1 below wereselected. Samples were prepared by melting the alloys in a highfrequency induction furnace, followed by annealing for thoroughelimination of strains. Measurement was made of the thermal expansioncoefficients (abbreviated as "TEC") of the alloy samples and thetemperatures at which said thermal expansion coefficients indicated arapid change, the results being set forth in Table 1 below. Measurementwas further made of the thermal expansion coefficients indicated by thealloy samples before and after the temperature of rapid deformation wasreached, and also of the thermal expansion coefficients indicated by thealloy samples over the temperature range from room temperature to 200°C.

                                      TABLE 1                                     __________________________________________________________________________                                                 TEC over a                                                                    range from                                          Temperature of                                                                        TEC before                                                                             TEC after                                                                              room temper-                     Sample                                                                            Chemical Composition                                                                         rapid change                                                                          said rapid                                                                             said rapid                                                                             ature to                         No. Fe Mn Ni Cu Cr in TEC (°C.)                                                                   change   change   200° C.                   __________________________________________________________________________    1   Bal.                                                                             6.3                                                                              -- -- -- No rapid de-                                                                          --       --       12.8 × 10.sup.-6                                                        /°C.                                         formation                                                  2   "  10.0                                                                             -- -- -- No rapid de-                                                                          --       --       15.5 × 10.sup.-6                                                        /°C.                                         formation                                                  3   "  15.8                                                                             -- -- -- 228     17.5 × 10.sup.-6 /°C.                                                     52.0 × 10.sup.-6 /°C.                                                     --                               4   "  18.0                                                                             -- -- -- 217     18.7     201      --                               5   "  20.3                                                                             -- -- -- 209     21.5     233      --                               6   "  25.0                                                                             -- -- -- 161     20.5     175      --                               7   "  28.9                                                                             -- -- -- 150     18.2     94.2     --                               8   "  30.0                                                                             -- -- -- 121     17.6     53.4     --                               9   "  40.8                                                                             -- -- -- No rapid de-                                                                          --       --       11.5 × 10.sup.-6                                                        /°C.                                         formation                                                  10  -- Bal.                                                                             11.0                                                                             18.3                                                                             -- No rapid de-                                                                          --       --       28.6 × 10.sup.-6                                                        /°C.                                         formation                                                  11  Bal.                                                                             1.05                                                                             9.11                                                                             -- 17.9                                                                             No rapid de-                                                                          --       --       17.8 × 10.sup.-6                                                        /°C.                                         formation                                                  12  "  1.22                                                                             20.3                                                                             -- 24.7                                                                             No rapid de-                                                                          --       --       16.9 × 10.sup.-6                                                        /°C.                                         formation                                                  13  "  0.4                                                                              36.7                                                                             -- -- No rapid de-                                                                          --       --       2.57 × 10.sup.-6                                                        /°C.                                         formation                                                  14  "  0.55                                                                             42.0                                                                             -- -- No rapid de-                                                                          --       --       5.40 × 10.sup.-6                                                        /°C.                                         formation                                                  __________________________________________________________________________

As apparent from Table 1 above, the samples Nos. 3 to 8 among thesamples Nos. 1 to 10 of high thermal expansion alloys used in theabove-mentioned experiment represent those whose thermal expansioncoefficients rapidly changed at the respective definite temperaturelevels. The samples Nos. 11 to 14 denote alloys of low thermalexpansion. The second Fe-Mn alloy of low thermal expansion used withthis invention has substantially the same thermal expansion coefficientas the alloy samples Nos. 11, 12 of Table 1. The alloy samples Nos. 11,12 were austenitic stainless steel SUS304 and SUS310.

The high thermal expansion alloy samples 2 and low thermal expansionalloy samples 3 shown in Table 1 were combined as shown in Table 2 belowto produce bimetal samples 1 (FIG. 1).

                  TABLE 2                                                         ______________________________________                                        Sample Nos. of Table 1                                                                             Modulus of                                                      High thermal                                                                             Low thermal                                                                              longitudinal                                     Sample expansion  expansion  elasticity                                       No.    alloy      alloy      (kg/mm.sup.2)                                    ______________________________________                                        15     10         13         12500    Control                                 16     1          13         14700    "                                       17     3          13         15700    Example                                 18     5          13         15400    "                                       19     7          13         15100    "                                       20     9          13         13400    Control                                 21     1          11         15800    "                                       22     3          11         17500    Example                                 23     5          11         17600    "                                       24     7          11         17600    "                                       25     9          11         14100    Control                                 26     1          12         16200    "                                       27     3          12         17800    Example                                 28     5          12         18300    "                                       29     7          12         18100    "                                       30     9          12         14700    Control                                 ______________________________________                                    

The bimetal samples were prepared in the following manner. The alloysamples of high and low thermal expansion were thermal forged into thickplates. The upper surface of each forged plate was ground and the lowersurface thereof was finished by brushing. Both alloy plates were bondedtogether by rolling at a temperature of 900° C. to 950° C. with bothplates made to have a thickness ratio of 1:1. After thus rolled, bothplates were further subjected to cold rolling. Annealing was repeated at1050° C., each time an assembly of laminated plates had its thicknessreduced by 35% by rolling in order to eliminate accumulated workstrains. A bimetal chip measuring 1 mm×10 mm was cut out of the samplethus prepared. Repetion of annealing for thorough elimination of workstrains is indispensable to suppress the occurrence of such harmfulphase (α' phase) as obstructs a rapid change in the thermal expansioncoefficient of a bimetal at a specified temperature (shown in Table 1).Said annealing may be undertaken before or after both alloy layers arebonded together.

Measurement was made of the modulus of longitudinal elasticity of thesamples Nos. 15 to 30, the results being also set forth in Table 2. Asseen from Table 2 above, the bimetal samples embodying this invention(Nos. 17 to 19, 22 to 24, 27 to 29) had a far more improved modulus oflongitudinal elasticity than the controls.

The bimetal samples of Table 2 (Nos. 15 to 30) were further tested ontheir deflecting property relative to temperature change to determinetheir behavior characteristics. Determination of the deflecting propertywas effected by measuring the displacement of the overhung free endportion of each sample 100 mm long, the results being presented inFIG. 1. The arrows shown therein indicate the direction in which thedeflection of the respective samples resulting from heating and coolingproceeded. The curve (a) of FIG. 1 denotes the deflecting property ofthe typical prior art bimetal (sample No. 15) and the curve (b)represents the deflecting property of the bimetal (sample No. 17) ofthis invention whose high expansion component was formed of a Fe-Mnalloy and chose low expansion component was prepared from a Fe-Ni alloy.The curves (c) to (e) indicate the deflecting property of the bimetalsof this invention (samples Nos. 27 to 29) whose high expansion componentwas formed of a Fe-Mn alloy and whose low expansion component wasprepared from austenitic stainless steel SUS310.

As seen from FIG. 1, the deflection of sample No. 15, that is, thetypical prior art bimetal (curve (a)) proceeded almost linearly relativeto temperature change. In contrast, the bimetals of this invention(curves (b) to (e)) were found to behave very sensitively at atemperature of rapid change in the thermal expansion coefficient andindicate hysteresis by heating and cooling. Further, FIG. 1 shows that atemperature of rapid deflection can be easily set at any desired levelby controlling the content of manganese, and that the temperatureadmitting of rapid deflection substantially falls within a high levelrange from 100° C. to 250° C. The curves (c) to (e) indicate that thethermal expansion coefficient of the bimetal of this invention whose lowexpansion alloy component was formed of austenitic stainless steelSUS310 did not rapidly change before the temperature of rapid deflectionwas reached, because both high and low expansion alloy components andsubstantially the same thermal coefficient, but that when thetemperature of rapid deflection was reached, then said bimetal verysensitively behaved, namely, showed a rapid deflection.

As mentioned above, the bimetal of this invention which is rapidlydeflected at a specified temperature is not rapidly fused to a contactdrive mechanism when directly used therewith, thereby effecting asatisfactory result. The bimetal of this invention indicates a rapiddeflection at a higher temperature than the prior art bimetal utilizingthe shape memory effect such as a Ni-Ti alloy. Moreover, the presentbimetal shows a rapid deflection over a wider temperature range morebroadened than has been possible in the past by properly controlling thecontent of manganese, chromium or cobalt.

EXAMPLE 2

A bimetal was prepared by the same manufacturing process as used inproducing the aforesaid Fe-Mn alloy with chromium and/or cobalt added toa high expansion alloy component in order to render the resultantbimetal anticorrosive. Experiments were made with this bimetal todetermine not only the deflecting characteristic as in the precedingcase but also the anticorrosive property. 1 to 20% by weight of chromiumand similarly 1 to 20% by weight of cobalt were added to theabove-mentioned Fe-Mn alloy to such extent that the total amount of amixture of chromium and cobalt indicated 2 to 20% by weight. The wholemass was melted in a high frequency induction furnace to preparesamples. These samples were also tested for the deflecting property.These high expansion alloy samples were bonded with low expansion alloysamples to provide bimetal samples which were expected to indicate ananticorrosive property. Test showed that the bimetal samples thusprepared had exactly the same deflecting property as the Fe-Mn bimetal.

Experiments on an anticorrosive property were undertaken with thesamples having a chemical composition shown in Table 3 below.

                  TABLE 3                                                         ______________________________________                                                           Tempera-                                                                      ture of  TEC                                                                  rapid    before said                                                                           TEC after                                 Sam- Chemical      change in                                                                              rapid   said rapid                                ple  Composition   TEC      change  change                                    No.  Fe     Mn     Cr  Co  (°C.)                                                                         (10.sup.-6 /°C.)                                                               (× 10.sup.-6 /°C.)     ______________________________________                                        101  Bal.   20     1   --  175    21.4    230 -102 " 20 2 -- 170 21.5 239                                               1                                   103  "      20     5   --  160    20.9    374                                 104  "      20     10  --  140    19.8    357                                 105  "      20     15  --  120    20.2    223                                 106  "      20     20  --  --     --      16.6*                               107  Bal.   20     --  1   176    19.5    268                                 108  "      20     --  3   164    21.1    283                                 109  "      20     --  5   169    18.6    267                                 110  "      20     --  10  158    20.7    251                                 111  "      20     --  15  154    20.3    173                                 112  Bal.   20     --  20  --     --      18.3*                               113  Bal.   20     1   1   168    21.0    211                                 114  "      20     2   1   160    20.3    205                                 115  "      20     2   5   161    19.2    272                                 116  "      20     5   1   157    18.7    272                                 117  "      20     5   5   151    19.8    232                                 118  "      20     10  3   171    20.1    128                                 119  "      20     10  5   152    19.9    102                                 120  "      20     3   15  143    18.2    68.0                                121  "      20     5   20  --     --      17.2*                               ______________________________________                                         *Thermal expansion coefficient over a change from room temperature to         200° C.                                                           

In the greater part of the experiments, the content of manganese wasrestricted to 20% by weight as shown in Table 3. The low expansion alloycomponents were prepared from the material of the aforesaid samples Nos.11, 14. Bimetal samples were provided by combinations of high and lowthermal expansion alloy components shown in Table 4

                  TABLE 4                                                         ______________________________________                                        Sample Nos.         Weight loss                                               Sample High expan-                                                                              Low expan-                                                                              due to corro-                                     No.    sion alloy sion alloy                                                                              sion (mg/cm.sup.2)                                ______________________________________                                        122    103        11        0.527     Example                                 123    103        14        0.580     "                                       124    101        11        0.872     Control                                 125    101        14        0.902     "                                       126    110        11        0.441     Example                                 127    110        14        0.408     "                                       128    107        11        0.911     Control                                 129    107        14        0.964     "                                       130    118        11        0.245     Example                                 131    118        14        0.251     "                                       132    113        11        0.621     Control                                 133    113        14        0.630     "                                       134     5         11        1.046     "                                       ______________________________________                                    

The corrosion test was carried out by dipping the bimetal samples for100 hours in 5% salt water at room temperature and measuring thesubsequent weight loss of said samples, the results being set forth inTable 4 above. As apparent from Table 4, the bimetals of this inventionwere subject to less weight loss by corrosion, namely, had a higheranticorrosive property than those of the control.

The bimetals of this invention prepared by the method of Example 2 werefound not only to indicate a rapid deflection at a specified temperaturebut also display a prominent anticorrosive property.

The bimetals of the invention are prepared, as described in theforegoing examples, from inexpensive material with a satisfactoryreversible property, and are adapted for use with great economicadvantage as a safety device such as a circuit breaker for householdelectric appliances and a thermal protector for various industrialapparatuses.

Apart from the above-mentioned application of a bimetal utilizing itsoriginal function, the bimetal of this invention is easily adapted to beused as an interleaf layer between two laminated nickel or copper platesor as a cover plate for either nickel or copper plate for improvementson the properties of electric appliances, for example, reduction ofelectric resistance.

What we claim is:
 1. A method of manufacturing a bimetal exhibiting ahysteresis and a rapid deflection over a predetermined temperaturerange, comprising the steps of:(a) providing a first metal component ofa high expansion metal alloy whose thermal expansion coefficient rapidlychanges from 21.5×10⁻⁶ /°C. or less to 50×10⁻⁶ /°C. or more at atemperature of between 100° C. and 250° C., said high expansion metalalloy being selected from a first alloy consisting of 15 to 30% byweight of manganese and substantially iron as the remainder or a secondalloy consisting essentially of 15 to 30% by weight of manganese, and amember selected from the group consisting of 2 to 15% by weight ofchromium, 2 to 15% by weight of cobalt and 2 to 20% by weight of amixture of chromium and cobalt and the balancce of iron; (b) providing asecond metal component of a low expansion metal alloy having a thermalexpansion coefficient substantially constant regardless of temperaturechanges; (c) annealing the first metal component repeatedly tosubstantially eliminate work strains contained therein; and (d) bondingtogether said first and second metal components.
 2. A method accordingto claim 1 wherein said first metal component is provided by thermallyforging said high expansion metal alloy.
 3. A method according to claim2, wherein said second metal component is provided by thermally forgingsaid low expansion metal alloy.
 4. A method according to claim 3,wherein said forging is carried out at a temperature of about 1050° C.to 1100° C.
 5. A method according to claim 1, wherein said bonding isconducted by hot rolling the first and second metal components.
 6. Amethod according to claim 5, wherein said hot rolling is carried out ata temperature of about 900° C. to 950° C.
 7. A method according to claim1, wherein said annealing step is commenced at 1050° C.
 8. A methodaccording to claim 1, wherein said annealing step is conducted aftersaid bonding.
 9. A method according to claim 8, wherein said annealingstep is commenced at 1050° C.
 10. A method according to claim 1,comprising cold-rolling the first and second metal components after saidbonding.
 11. A method according to claim 1, wherein said high expansionmetal alloy is said first alloy.
 12. A method according to claim 11,wherein said first alloy contains 15 to 25% by weight of manganese. 13.A method according to claim 12, wherein said low expansion metal alloyhas a thermal expansion coefficient substantially the same as that ofsaid high expansion metal alloy exhibited at a temperature lower thanthat at which the thermal expansion coefficient of the high expansionmetal alloy rapidly increases.
 14. A method according to claim 13,wherein said low expansion metal alloy is an austenitic stainless steel.15. A method according to claim 1, wherein said high expansion metalalloy is said second alloy.
 16. A method according to claim 15, whereinsaid second alloy contains 15 to 25% by weight of manganese.
 17. Amethod according to claim 16, wherein said second alloy contains from 2to 20% by weight of a mixture of chromium and cobalt and the balance ofiron.
 18. A method according to claim 15, 16 or 17, wherein said lowexpansion metal alloy has a thermal expansion coefficient substantiallythe same as that of said high expansion metal alloy exhibited at atemperature lower than that at which the thermal expansion coefficientof the high expansion metal alloy rapidly increases.
 19. A methodaccording to claim 16, wherein said low expansion metal alloy is anaustenitic stainless steel.